Researchers from the University of Granada in Spain examined 962 pregnant women, half of whom performed light to moderate exercise 50 to 55 minutes three days a week, and half of whom didn't follow any exercise plan. Turns out, the exercisers were 40 percent less likely to gain too much weight. What's more, obese and overweight women who exercised during their pregnancies were 86 percent less likely to have babies with macrosomia than those who didn't.

Macrosomia (also known as "Big Baby Syndrome") is a condition in which babies weigh at least 8 pounds, 13 ounces at birth (the average birth weight is about 7 pounds). Macrosomia increases the chance of damage to your birth canal, puts your baby at a higher risk of injury during vaginal delivery, and makes you more likely to need a C-section. Plus, babies with macrosomia have an increased risk of low blood sugar, respiratory distress, and jaundice.

Macrosomia or not, more than half of women gain more weight during pregnancy than they should, says a study published in Obstetric Medicine. (Check out our BMI calculator to see how much you should gain.)

Not to fear. Here's the easy exercise plan they followed in the study:

Stretch it out.

Part of the 50-55-minute sweat session included a 10-minute warm-up and 10-minute cool-down, involving stretching. "It's important to stretch your muscles and connective tissues during pregnancy," says Marta Montenegro, M.S., C.S.C.S., and exercise physiologist. "The extra weight women carry during pregnancy throws off the whole body's alignment, so joints and muscles are overly taxed." To curb joint and muscle pain, you don't need to stretch for more than a few minutes, you just need to do it regularly, says Montenegro.

Resistance-train twice a week.

The women in the study lifted weights twice a week, exercising their arms, shoulders, legs, and ankles for just under half an hour. During your pregnancy, Montenegro suggests using strength machines rather than free weights (there's less chance of injury) and performing one to three sets of 12 to 15 light reps. Note: After your first trimester, avoid any exercises that involve laying flat on a bench or the floor, which could lead to sudden blood pressure changes.

Do a light aerobic exercise once a week.

The study participants did an aerobic dance workout once a week for 30 minutes. Get the benefits by swimming, walking, or spinning for the same amount of time.

Don't overexert yourself.

No matter the exercise, the women in the study weren't exactly exerting themselves Jillian Michaels-style. A good rule of thumb for assessing your exertion level: You should be able to say a sentence without gasping for breath.

Pretty doable, right? Remember: Every little bit of low-intensity exercise counts, so find a workout you enjoy, and stick with it.